Regenerative piano



y 1935. J. H. HAMMOND, JR 2,001,723

REGENERATIVE PIANO Filed June 16, 1932 AMPLIFIER WEN TOR.

A TTORNEYS Patented May 21, 1935 UNITED STATES PATENT OFFICE 22 Claims.

This invention relates to musical instruments and more particularly to a musical instrument having a sounding board and strings and devices for amplifying the vibrations of said sounding board and said strings.

The invention also provides a regenerative cycle for picking up and amplifying these vibrations and returning the amplified vibrations to the sounding board. Means is also provided for manually adjusting the relative amount of energy picked up from the sound board and strings and for mixing them together before amplification.

A filter may be provided in the sounding board pick up circuit for eliminating the anti-nodal frequency of the sound board at the point at which the pickup is located, thus preventing disagreeable howling, which would otherwise occur when the note of this frequency was struck.

A further object of the invention is the provision of means for eliminating the initial peak or thump when the notes are struck.

The invention also consists in certain new and original features of construction and.combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which Fig. 1 is a front elevation partly in section of a piano with a. diagrammatic showing of the amplifying devices associated therewith.

Fig. 2 is a cross sectional detail of one of the string pickup devices.

Like reference characters denote like parts in the several figures of the drawing.

In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the form of the invention shown in the accompanying figures, a grand piano II is provided with the usual strings I2 mounted in a frame I3. This piano is provided with the usual sound board I4 and diagonal braces I5. Mounted on these braces is an electromagnetic pickup device I5, the armature of which is connected by a rod II to the sounding board I4. This pickup device is connected to a filter circuit I8 and to 10W pass filter I 8, the other side of which is connected across a potentiometer 2 I.

The filter I8 eliminates the anti-nodal frequency at the point where the pickup I6 is connected and the low pass filter I9 eliminates the 5 higher frequencies which are better handled by the string pickup system as hereinafter described more in detail.

Mounted on bars 25 which are carried by the frame I3 is a plurality of electromagnetic pickup devices 21, which consist of permanent magnets 28 (Fig. 2), to the ends of which are screwed two spools of magnetic material 3I and 32. Wound upon these two spools are two coils 33 and 34. The spools 3| and 32 are located adjacent to the strings I2. The windings of the coils 33 and 34 are serially connected and the pickup devices 21 are connected in series to a potentiometer 31.

The potentiometers 2| and 31 are connected to the input circuits of two space discharge devices 43 and 44 which are biased by a battery 45. A battery 46 heats the filaments of these two devices. The output circuits of the devices '43 and 44 include a B-battery 41 and the primary of a transformer 48. One side of the secondary of the transformer 48 is connected by a conductor 49 to the grid of control tube 52 and also through an audio pass blocking condenser 5I to the grid of a space discharge amplifier device 52.

The other side of the secondary of transformer 48 is connected by wire 53 to ground at 51, thence through ground to point I51, through 0 batteries 65 and 65, double throw switch I65 to the cathode of amplifier tube 52 and through C battery 65 to the cathode of control tube 62. Resistance 64 connects ground I51 to the heaters of tubes 52 and 62.

For controlling the action of amplifier tube 52 the control tube 62 is provided, which supplies current to a. biasing resistance 58 which controls the potential of the grid of amplifier tube 52 and hence its gain ratio.

The output circuit of control tube 62 includes B batteries 61, 69 and the primary of transformer 45 58. The secondary of transformer 59 is connected in circuit with biasing resistance 58 and with a rectifier GI through double-pole, doublethrow switch 68.

For controlling the time action of biasing resistance 58 small condenser 55, large condenser 54 and a resistance 56 are provided. Doublethrow switch 50 selectively connects condensers 54 and 55 across biasing resistance 58. Heating current is supplied to tubes SI and 62 through 4;

transformer 63 which is supplied by a source of alternating current indicated by I63.

The output circuit of amplifier tube 52 includes a filter circuit made up of inductance I2 and capacitances II and I3, capacitance II having connected in parallel therewith a resistance I0 and the primary of transformer 68. The secondary of the transformer 68 feeds an amplifier indicated by I5, the output of which feeds loud speaker I6.

' The loud speaker I6 may be of the so-called dynamic type whose sound propagating element or armature (not shown) has no connection with the sounding board M. The frame of the loud speaker is connected to the sounding board I4 which may be provided with a hole I1 at the mouth of the loud speaker 16.

The loud speaker 76 feeds energy'back to the sounding board I4 directly by its mounting thereon and indirectly through the strings I2 due to acoustic coupling.

It has been discovered from experiment with piano sounding boards and electric loud speakers that an acoustic coupling can be secured through proper geometrical disposition of the sounding board and loud speaker and that through this coupling the normal piano tone can be made to sound through the interaction of the sounding board and the loud speaker even though the diaphragm or sound propagating element of the loud speaker is not in physical contact with the sound board.

The filter circuit made up of elements II, 72 and I3 acts to eliminate any high frequency harsh noises from being fed back to the loud speaker I6.

The system shown in Fig. 1 may be operated in two ways. First, with the reversing switch thrown to the right, the time action switch 50 up and the C-battery switch I65 to the right, to produce a rapid anti-dynamic multiplier action for controlling the thump; and second, with the reversing switch I50 to the left, the time action switch 58 down and the C-battery switch I65 to the left to produce a slow action dynamic multiplier for thump control.

Taking the first way for example, the piano is played in the usual manner and the vibrations of the sound board I 4 and strings I2 are picked up by the pickup devices I6 and 2?. The energy from the former passes through the filters I8 and M, which eliminates the anti-nodal frequency of the sound board at the point where the pickup is located, and also any of the high frequencies which may be picked up from the sound board. The output from this filter is thenfed through the potentiometer 2! to the input circuit of the device Q3.

The vibrations of the strings under the pickup devices 2'5 causes these devices to pick up energy from these strings and feed it through the potentiometer 3'5 to the input circuit of the device 44. The potentiometers 2i and 37 are so adjusted that the relative amount of energy picked up from the sound board and the strings is in the proper proportion to produce the desired musical results. The energy from these two sources is then amplified by means of the devices 43 and M and fed to the transformer Q8. The outputvoltage from this transformer then passes through the stoppage condenser 5i to the input circuit of the amplifier device 52 and also to the input circuit of the control device 62.

The output current from the control device 62 then passes through the transformer 59 and is rectified by the rectifier GI, the rectified current flowing through the resistance 51 in the direction of the arrow 8|. This causes a potential drop across this resistance which is proportional to the current flowing through it and therefore to the signal strength. This causes a negative potential to be impressed upon the grid of the amplifier device 52 thus increasing its internal impedance and, therefore, decreasing its amplification factor or gain ratio.

It is thus seen that with increasing signal strength the amplification factor of the device will be decreased, so that, when there is a sudden increase of energy due to a note being struck, the amplification factor will be small, thus preventing a disagreeable thump being produced in the music.

The amplified current from the amplifier device 52 then passes through the transformer 68 to the amplifier 75, where it is amplified and fed to the loud speaker 76. The condensers II and I3 and the inductance 12 form a filter network for cutting out high frequency noises and disturbances.

In this way the high frequency notes of the piano can be picked up directly from the strings and combined in any desired proportion with the lower notes, which are picked up from the sound board. Thus the high notes, which are usually weak and which do not affect the sound board as much as the lower notes, can be brought out more fully, and a better balance of tone may be produced. The circuit consisting of the condenser 55 and the resistance 58 forms a delay action system, the time of action of which is very rapid due to the fact that the condenser 55 has a small capacity, so that the anti-dynamic multiplier comes into action the instant that the note is struck, to reduce the amplification factor, so as to prevent a sudden surge of energy which would produce a disagreeable thump. As the note of they piano dies away, the current flowing through the resistance 58 decreases, thus decreasing the negative bias on the device 52 which increases its amplification factor, thus tending to sustain the note for an appreciable length of time.

In the second method of operation, with the reversing switch 60 to the left, the time action switch 50 down, and the C-battery switch I to the left, the current from the rectifier GI will flow through the resistance 58 in the direction of the arrow 82, the resistance drop opposing C-bat teries 65 and 66 thus tending to decrease the bias on the amplifier 52 with increase of signal. This action is slow, however, due to the large capacitance of the condenser 54, so that during the period immediately after the striking of a note, when the energy received from the pickup devices is very high, the amplification factor of the amplifier 52 will be small, thus preventing a sudden surge of energy to the amplifier l5, and a disagreeable thump in the music. As the note of the piano dies away, the amplification factor of the amplifier 52 will increase to a maximum and then decrease again. In this way a sudden thump is prevented and the note is prolonged due to the energy stored in the large condenser 54, which causes the amplification factor of the amplifier 52 to remain large for an appreciable length of time.

It is possible to vary the number of turns in the windings 33 and 34 of the magnets 21 so as't'o vary the amount of pick up from each magnet to produce a balanced effect from the entire group of string pick ups.

Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited. to any specific construction, but might be embodied invarious forms without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. In combination with a musical instrument having a sounding board and strings, pickup devices associated with said soundboard and said strings. and adapted to pick up energy of vibration therefrom, means for combining and amplifying said energies and means for applying said amplified energy to said sounding board.

2. In combination with a musical instrument having a sounding board and strings, pickup devices associated with said sound board and said strings, and adapted to pick up energy of vibration therefrom, means for combining and amplifying said energies, a loud speaker, and means for applying said amplified energy to said loud speaker.

3. In combination with a musical instrument having a sounding board and strings, pickup devices associated with said sound board and said strings and adapted to pick up energy of vibration therefrom, means for eliminating a particular frequency from the output circuit of said sound board pick up, means for combining and amplifying said energies and means for applying said amplified energy to said sounding board.

4. In combination wit-h a vibratory musical instrument, pickup devices associated therewith and adapted to pick up energy of vibration therefrom, means for amplifying said energy, means associated therewith operative only for decreasing the initial surge of energy due to the percussive action of said musical instrument without affecting the volume for sustained high energy vibration, and means for applying said amplified energy to said musical instrument.

5. In a piano having a sound board and strings, pickup devices associated with said sound board and said strings and adapted to pick up energy of vibration therefrom, a filter network in the circuit of the sound board pickup device for eliminating the resonant frequency of the sound board at the point of pick up, means for combining the energy from the sound board and string pick up in any desired proportion, means for amplifying said combined energy and means for applying said amplified energy to a loud speaker located adjacent said sound board.

6. In a musical instrument, means for picking up the vibrations therefrom, means for amplifying said vibrations and gain control means for decreasing the gain ratio of said amplifying means when the input signal strength-is greatly increased.

7. In a piano, means for picking up the vibrations therefrom, means for amplifying said vibrations and means for decreasing the gain ratio of said amplifying means when there is an increase of energy and increasing the gain ratio of said amplifying means when there is a decrease of energy.

8. In a piano, means for picking up the vibrations therefrom, means for amplifying said vibrations, gain control means for increasing the gain ratio of said amplifier with increase of energy picked up from the piano, and timing means for delaying said increase of the gain ratio for a predetermined interval of time, in order to eliminate the thump in the music.

9. In a musical instrument having strings and a sound board, a pickup device connected to the sound board, a sound propagating device, means for amplifying energy from said pickup device and feeding it to said sound propagating device, and means for filtering out anti-nodal frequencies of the sound board.

10. In a musical instrument having strings and a sound board, means for picking up high frequency tones from said strings, means for picking up low frequency tones from said sound board, an amplifier fed by said pickup means, a translating device fed by said amplifier, and means for regeneratively connecting the output and input of said amplifier.

11. In a musical instrument, a plurality of strings tuned to different pitches, percussive devices for setting said strings into vibration, a piano keyboard controlling said percussive devices, electric pick-ups for said strings, an amplifier fed by said pick-ups, a loud speaker fed by said amplifier, and limiting devices operative only for limiting the initial rush of energy to said loud speaker when said strings are engaged by said percussive devices.

12. In a musical instrument, a plurality of strings tuned to different pitches, devices for setting said strings into vibration, a piano keyboard controlling said devices, an electric pick-up device for picking up energy caused by vibration of said strings, an amplifier fed by said pick-up device, a speaker fed by said amplifier, and limiting devices operative only for limiting the initial rush of energy to said speaker when said strings are vibrated.

13. In a musical instrument, a plurality of vibratory elements tuned to different pitches, means for operating said vibratory elements, an electric pick-up for picking up said vibrations, a dynamic modifier fed by said pick-up and a translating device fed by said dynamic modifier.

14. In a musical instrument, a plurality of vibratory strings tuned to different pitches, a piano keyboard for operating said strings, an electric pick-up for picking up vibrations from said strings, a dynamic amplifier fed by said pick-up and a speaker fed by said dynamic amplifier.

15. In a mus cal instrument having a vibratory element capable of vibrating at a plurality of frequencies, means for impressing vibrations on said vibratory element, and filter means for eliminating anti-nodal frequencies.

16. In a musical instrument having a vibratory element capable of vibrating at a plurality of frequencies, means for impressing forced vibrations on said vibratory element, an electric pick-up fed by said vibratory element, a speaker fed by said pick-up, and filter means between said pick-up and said speaker for eliminating anti-nodal frequencies of said vibratory element.

17. In a musical instrument, a plurality of strings tuned to different pitches, percussive devices for setting said strings into vibration, a piano keyboard controlling said percussive devices, electric pick-up devices for picking up energy from said strings, an amplifier fed by said pick-up devces, a speaker fed by said amplifier, and filter means between said pick-up devices and speaker to discriminate against the higher frequencies.

18. In a musical instrument, a plurality of strings tuned to different pitches, devices for setting said strings into vibration, electric pick-up devices for picking up energy from said strings, an amplifier fed by said pick-up devices, a translating device fed by said amplifier, and means between said pick-up devices and translating device to discriminate against the higher frequencies.

19. In a musical instrument, sound initiating elements, a sound re-enforcing element, pick-up devices associated with said elements, a translating device and means for combining the energy from said pick-up devices and applying it to said translating device.

20. In a musical instrument, an element for originating a musical note, a resonating element, a translating device and means for picking up and then combining the vibrations of both sa'd elements and applying them to said translating device.

21. In a musical instrument, a sound initiating element, a resonator, pick-up devices associated with said element and said resonator, a dynamic modifier fed by the combined output of said pickup devices and a translating device fed by said modifier.

22. In a musical instrument, a sound initiating element, a resonator, energy pick-up devices associated with said element and said resonator, a translating device, means for combining the energies from said pick-up devices and applying said combined energy to said translating device and means for varying the proportions in which said picked-up energies are combined.

JOHN HAYS HAMMOND, JR. 

